Under pressure from their rivals, the leading Republican presidential contenders defended their conservative credentials on abortion, gun control and tax cuts in a feisty debate Tuesday night.

"Republicans should be uniting" to defeat the Democrats, implored former New York Mayor Rudy Giuliani, rather than stressing their differences with one another.

Giuliani, pressed repeatedly on his support for abortion rights, wasn't the only contender to field pointed questions.

Former Massachusetts Gov. Mitt Romney conceded he had signed legislation banning assault weapons but said, "Let's get the record straight." He said he is a supporter of the rights of gun owners under the Second Amendment.

Arizona Sen. John McCain of Arizona said he would make sure that President Bush's tax cuts are made permanent, even though he said he had voted against because they were not accompanied by spending cuts.

"If we don't make them permanent then every business farm and family will have to adjust their budgets to what is in effect a tax increase," he said.

All three men sought to stand their ground — and protect their standing in the presidential race — in a 90-minute debate at the University of South Carolina.

The 10 men on the debate stage differed only by degree when it came to the familiar Republican themes of tax cuts, reduced spending and a smaller federal bureaucracy.

Giuliani called for "Reagan-like budget cuts across the board" of between 5 percent and 20 percent, and Tommy Thompson said he had cast many vetoes while governor of Wisconsin to hold down spending.

In a change from the campaign's first debate, on May 3, some of the contenders who lag in the polls jabbed at the front-runners.

That wasn't all, he added quickly, saying his rivals had undergone recent conversions on abortion and other issues.

"I trust those conversions when they happen on the road to Damascus and not on the road to Des Moines," he said, contrasting the biblical with the political.

Former Virginia Gov. Jim Gilmore bore in, as well. "Some of the people on this stage were very liberal in characterizing themselves as conservatives, particularly on the issues of abortion and taxes and health care," he said.

He singled out Giuliani for his position on abortion and said another rival, Mike Huckabee, had raised taxes while serving as governor of Arkansas.

Huckabee responded that the state raised taxes in response to a court order and said he had cut taxes repeatedly.

On defense for much of the evening, Giuliani switched gears nearly an hour into the debate, challenging Rep. Ron Paul's suggestion that the U.S. bombing of Iraq had contributed to the terrorist attacks of 2001.

As mayor of New York at the time of the attacks, Giuliani said sternly, "I don't think I've ever heard that before, and I have heard some pretty absurd explanations."

His rebuke to Paul drew some of the loudest applause of the night from the partisan audience.

There were few moments when the Republicans sought to turn the campaign spotlight on the Democrats, who are embarked on a drive to win back the White House after President Bush's two terms.

"We've had a Congress that's spent money like John Edwards at a beauty shop," Huckabee said, mocking the Democratic presidential hopeful's penchant for $400 haircuts.

He did not mention that until January, Congress has been under the control of Republicans for a dozen years.

Giuliani combined his plea to unite against the Democrats with an attack on New York Sen. Hillary Rodham Clinton as an apostle of big government.

"Those are the things that we should be debating and Republicans should be uniting to make certain what the liberal media is talking about, our inevitable defeat, doesn't happen," he said.

Not everyone was convinced.

Rep. Duncan Hunter, the top Republican on the House Armed Services Committee, noted his experience on military matters and challenged those on stage with him to lay out their credentials to be commander in chief.

Hours before the debate, candidates responded to the death of the Rev. Jerry Falwell, the television evangelist who founded the Moral Majority and was a force in conservative politics.

If the first debate was framed by the spirit of Ronald Reagan, then tonight's gathering in the heart of the Bible Belt takes place in the shadow of Falwell's death, reports CBS News chief White House correspondent Jim Axelrod.

"These candidates have to be concerned about the way in which they appeal to what we now call 'value voters,' religious voters, people who shared the values that Jerry Falwell championed, because he got them active in politics," said Republican activist David Keene.